Well you can use Bench Marking software like 3DMark, Aquamark, Lightsmark, Furmark, etc.

Or you can use a lay method for general testing in games like Sleeping Dogs, SS4, and many other games provide internal benchmark options where you can do bench marks to see differences.

else you can use any FPS Counter software in a game to see the difference when playing the game. Many game like Battle Field provides the command line option to enable FPS showing which can be handy.

OR you can use Radeon Pro, which can hook onto d3d9 and d3d10 games to show you the FPS count while playing....

Remember.., make sure all settings in CCC and games are same while performing tests with different Drivers.

I will use the fps test in css.

Device manager doesn't want to update the generic driver. I installed the inf by myself, is that ok?

edit2 : I did some group policy trick to prevent windows from installing the generic driver, then I chose the modded driver folder and before clicking on "next" I disabled the policy and windows installed the new driver.